With increasing demand for small, high-power light emitting elements, demand for flip-chip type large-area light emitting elements having good heat dissipation efficiency is also increasing. In a flip-chip type light emitting element, since electrodes are directly bonded to a secondary substrate, a wire for supply of external power source is not used, thereby providing better heat dissipation efficiency than a lateral type light emitting element. That is, since heat is transferred to the secondary substrate side even upon application of high density current to the flip-chip type light emitting element, the flip-chip type light emitting element can be used as a high power light source.
On the other hand, for miniaturization of light emitting elements, there is increasing demand for a chip-scale package which allows a light emitting element to be used as a package by eliminating a separate process of packaging the light emitting element in a housing. For the flip-chip type light emitting element, the electrodes act like leads of the package and thus can be advantageously applied to the chip-scale package.
In fabrication of a light emitting element using a chip-scale package, high density current can be applied to the chip-scale package. Recently, with increasing demand for high power products, drive current applied to the chip-scale package is also increasing. As the drive current applied to the chip-scale package increases, heat generated from a light emitting diode chip also increases, thereby causing thermal stress to the light emitting element. Moreover, junction temperature is also increased due to the increased heat, thereby causing deterioration in reliability of the light emitting element.
In addition, a light emitting element can be manufactured by disposing a plurality of chip-scale package type light emitting cells connected to each other in series or in parallel on a substrate. In the structure of the light emitting cell realized using the plurality of light emitting cells, a non-luminous region is formed between the light emitting cells, thereby causing poor luminous efficacy at the center of the light emitting element.
To fulfill recent demand for high power products, various studies for increasing luminous efficacy of the chip-scale package have been carried out. Even in the case of fabricating a light emitting element using plural light emitting cells, technology for maximizing luminous efficacy of the light emitting element is required.
In application of a plurality of light emitting elements connected to each other in series to a headlight of an automobile, relatively high voltage can be applied to opposite ends of the plurality of light emitting elements connected to each other in series. When the light emitting elements connected in series do not have forward voltage characteristics, an excessively high voltage can be applied to a light emitting diode having low forward voltage, whereby the light emitting element can exhibit low stability, thereby causing deterioration in product reliability.